Synchronizing control apparatus for multiple engines



R. L. WILSON June l5, 1948.

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SYNCHRONIZING CONTROL APPARATUS FOR MULTIPLE ENGINES Original Filed Oct. 12, 1943 4 Sheets-Sheet 4 Fig. 6.

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Patented June 1s, 194s SYNOHRONIZING CONTROL APPARATUS FOR MULTIPLE ENGINES Rosser L. Wilson, Mahwah, N. J., assignor to American Brake Shoe Company, Wilmington, Del., a corporation of Delaware Original application October 12, 1943, Serial No.

505,938. Divided and this application September 15, 1947, Serial No. 774,081

4 Claims. 1

This application is a division of my co-pending application Serial No. 505,938, filed October 12, 1943.

This invention relates to control apparatus for use in governing the relative speeds of moving parts of machinery such as shafts and the like, and particularly it relates to such control ap- Y paratus for establishing and maintaining a suby stantially synchronous or other desired speed relationship between two or more such moving parts such as two or more rotating shafts which otherwise `Jvould operate independently of each other.

The need for control apparatus of the aforesaid character may arise in any situation where it is desirable that the variantly adjustable operating speed of a particular member, such as a shaft, serves as a standard with which the operating speed of one or more other independently driven shafts or the like is to be correlated. In such instances the shaft which is to constitute the standard may serve merely as a variable speed control shaft for one or more engines, motors or the like, cr it may constitute the shaft of a master engine or motor of a group of two or more similar engines or motors which are to be operated in a correlated relationship. y

The use of one or more engines as the driving power for an airplane affords one typical situation where control apparatus of the aforesaid character is desirable, for whether the airplane be driven by a single engine, or by two or more similar engines, the maintenance of the desired speed of operation such engine or engines is extremely difficult because of the rapid and eX- tremely wide variance of the factors such as wind resistance, attitude of flight or the like, which affect and vary the operating speed of such engine or engines. Thus, in a single engine airplane, a Variable speed electric motor may be used as a standard from which the speed of operation of the single engine may be automatically governed by control apparatus of the aforesaid character; while in an airplane having a plurality of engines, such control apparatus may serve to coordinate the speed of all of the engines with the speed of such a variable speed electric motor, or if desired, a particular one of the engines may serve as the Variable standard of speed, and such control apparatus may serve to coordinate the speed of the other engines with the one'engine which in such an event constitues the standard or master engine. It is therefore an object of this invention to enable automatic yet adjustable control of the speed of one 2 or more engines to be attained in such a manner that control of the speed thereof is simplified, and if desired the control of the speed of all of the engines of a multi-motored airplane may be adjusted through manipulation of but a single control means.

Where such control apparatus is used as aforesaid to control the operating speed of one or more airplane engines, it is oi course desirable that the apparatus be rugged in character, re1- atively light in weight, and dependable and accurate in its operation or correlation of the secondary shafts or engines with the master shaft, and in the patent to Wilson No. 2,232,753, patented February 25, 1941, several formsof control apparatus are disclosed which meet these fundamental requirements. It is, however, an important object of this invention to enable further improvement of the operating characteristics of such control apparatus to be attained.

Control apparatus of the aforesaid character attains the desired speed correlation through the control of power operated speed adjusting mechanism which, upon detection of undesired speed variance, acts to adjust the speed of the secondary shaft or the like in such a sense as to tend to re-establish the desired speed relationship. As a practical matter, the power operated speed adjusting means may be arranged to attain the speed adjustment in different ways which are determined to a great extent by the fleldin which the apparatus is used. For example, in an airplane engine, the speed may be varied by adjustment of the pitch of the propeller driven thereby, or by adjustment of the fuel supply means such as a carburetor, or by adjustment of other means which affect engine speed. Where resort is had to the adjustment of the propeller pitch, the power means for operating the same may in many instances constitute a standardized part of the equipment to which the control apparatus as a whole must be related and adapted so as to attain the desired accuracy of speed correlation.

'An important problem encountered in the use of control apparatus of the aforesaid character centers about the inherent conditions which make the engine or other shaft-driving means more responsive to correction in one direction than in the other, for it will be clear that because of the load or other resistance which is usually effective upon a driven member or shaft, a reduction in the speed of the shaft may be eected more easily and quickly than an increase of the shaft speed. It is therefore a further object of this invention to enable control apparatus of the aforesaid character to compensate for such differences in the responsiveness of the controlled mechanism to speed correction in opposite directions, thereby to further increase the accuracy of correlation attained by the apparatus.

While control apparatus of the kind to which this invention relates operates under normal service conditions to maintain the speeds of the compared members or shafts within the operating tolerance for which the apparatus is designed, it must be recognized that circumstances may arise where the speed difference is relatively great, and to enable such apparatus to establish or re-establish the desired speed relation under such conditions is a furtherv object of this invention. When such a great speed differential is present it is usually quite important that the desired speed relationship be re-established as rapidly as possible, and to enable this to be accomplished in control apparatus which operates within a small tolerance is another important object of the invention. Further and related objects of the invention areto render the rate of correction of the speed of the master shaft dependent upon the magnitude of the existing speed differential, and to enable the rate of such correction to be varied in accordance with the direction in which the correction is to be applied.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments and the principle thereof and what is now considered to be the best mode of applying that principle. Other embodiments of the invention embodying the same or equivalent principle may be used and structural changes may be made as desired by those skilled in the art without departing from vention and the purview of the appended claims.

In the drawings:

Fig. 1 is a schematic wiring diagram illustrating a control apparatus embodying the features of the invention and adapted for correlating the speed of one or more secondary shafts with the speed of a master shaft;

Fig. 1A is a fragmentary view of an alternative form of apparatus that may be utilized in place of a portion of the apparatus shown in Fig. 1:

Fig. 2 is a wiring diagram illustrating another embodiment of control unit that may be utilized in the control apparatus of Fig. 1;

Fig. 3 is a wiring diagram illustrating still another control unit that may be utilized in the control apparatus of Fig. 1;

Fig. 4 is a wiring diagram illustrating another form of control unit embodying the invention and adapted to be used in the control apparatus of 'l Fig. 1:

Fig. 5 is a fragmental wiring diagram illustrating means whereby the controlling action attained with the apparatus of Figs. 1. 2, 3 and 4 may be further rened;

Fig. 6 is a fragmental wiring diagram showing a form of means for increasing the accuracy of control attained by the mechanism of Figs. 1 and 2, 3 and 4 Fig. 7 is a. diagrammatic view illustrating another form of actuatcr which may be utilized; and

Figs. 8 and 9 are schematic wiring diagrams illustrating further embodiments of the invention.

In the various embodiments of the invention the present inor more engines its main shaft 23 to drive a load chosen for disclosure herein the invention is particularly adapted for governing the speed of one of an airplane, but it will be recognized that these embodiments of the invention are of general utility, and may be eiectively employed in any circumstance where correlation of the speeds of two or pendently driven shafts is desired. Thus in the embodiment of the invention illustrated in Fig. l of the drawings, a plurality of shafts 20M, 2li-l, '2D-2, 20-3 and 20-N are shown, and means are provided for correlating the speeds of these shafts so that one of the shafts, as the shaft 20M, constitutes the master shaft, and the other shafts 2li-l, 20-2, 2li-3 and 2li-N are maintained at speeds which bear a predetermined relationship to the master shaft 20M. 'I'his predetermined relationship may, as in the present case, be a substantially synchronous relationship, or, by the use of gearing, any other desired speed relationship between two or more shafts or the like may be maintained.

In the attainment of the desired speed relationship between the several shafts, the master shaft 20M is driven at the desired speed by driving means such asa variable speed controlling element 2| which may take any desired form such as a variable speed electric motor or a variable speed engine. Thus, as illustrated in Fig. 1 of the drawings, itis contemplated that the master shaft 20M shafts 2li-I, '2U-2, 20-3 and 20-N are to be correlated, and hence the variable speed controlling element 2 l' may be in the form of a relatively small variable speed electric motor. The other or secondary shafts 2li-I, l2li-2,4 20-3 and 2li-N, may be driven by individual variable speed driving internal combustion engines such as the engine indicated at 22 in Fig. 1, which may take the form of an airplane engine operating through 24 such as an airplane propeller. The drive from the engine shaft 23 to the related shaft 20-l may, of course. be direct, or as in the present instance, may be attained through gearing 25. The speed of each such engine, and hence of the associated shaft as 2li-l, may be varied by adjustment of the load or the propeller pitch, or by adjustment of the fuel supply means, and this may be accomplished by operation of conventional speed governing means such as the mechanism of a variable pitch propeller, or by operation or adjustment of the fuel pump or carburetor of the engine. Thus in Fig. 1 of the drawings such governing mechanism is indicated generally as 26, and it is by automatic operation or adjustment of such governing mechanism 26 that the desired correlation of the secondary shaft 20-i with the master shaft 20M is attained under the present invention. The governing mechanism 2G, of course, is adjustable in two directions so as to enable the speed of `the secondary shaft 20-I to be increased or decreased in accordance with the sense of the variance between the speeds of this shaft and the master shaft 20M, and such actuation may be eected in different ways, as, for example, by a reversible electric motor 21 having an operating connection 28 with the speed governing mechanism 2'! and in Fig. 1 the speed adjusting means may be taken as being a fuel adjusting means and is therefore shown as being connected to the engine at 26'.

It will Ibe understood that the reversible electric motor 21 and the parts associated therewith are illustrative of an arrangement to which resort may be had for the effecting operation of the governing mechanism 26 and as a further example of means which may be employed for this purpose, resort may be had to the arrangement shown in Fig. 1A wherein a two-way hydraulic actuator 29 is provided which is controlled by a two-way solenoid valve operator 30, the hydraulic actuator 29 being connected to the governing mechanism 26 through a connection as 3|, and the governing mechanism 26 is in this instance associated 26" with'the load 24 so as to adjust the speed of the engine 22 by variation of the load, such adjustment of the load being attained by adjustment of the propeller pitch. Moreover,

it will be evident that the electric motor 21 may is provided with similar brushes 4L' 42 and 43 driven in each instance by the respective one of the secondary shafts with which the particular commutator switch is associated.

The three brushes 4l, 42 and 43 of each secondary commutator switch, as Sl, are associated with the related control unit, as CUI, by means be utilized for adjustment of the propeller or other load, or the hydraulic means 23 may be arranged in some instances so as to adjust a fuel supply means and thereby adjust the engine speed.

The mechanism which has thus been described for driving the secondary shaft 2li-l, and for adjusting the speed at which the shaft -l is driven, may be said to constitute a driving and speed adjusting unit 35-I for the secondary shaft 2li-I, the elements which make up such unit being clearly indicated in Fig. 1 by being included within a block defined by dot-dash lines and indicated by the reference character 3ft-l; and similar driving and speed adjusting units 3.5-2, 35-3, 35-N, similarly associated with the secondary shafts 2li-2, 2li-3, and 2li-N, respectively, have been illustrated in Fig. 1 by blocks bearing such reference characters.

Under the present invention the speed of each secondary shaft as 2li- I is compared with the speed of the master shaft 20M to detect the presence and sense of any undesired variance between the speeds of the secondary shafts and the master shaft, and upon such detection of undesired speed variance in respect to a particular secondary shaft, the speed governing means of the associated engine is adjusted in a controlled manner in the direction required to re-establish the desired speed relationship. In accomplishing such adjustment an individual control unit CUl is provided which governs the operation of the motor 21 of the unit 35-l; and similar control units CU2, CU3, and CUn are similarly provided for and associated with the units 35-2, 35--3 and 35-N, respectively. Such control units CUI, CU2, and CU3 and CUn are, in turn, associated with detecting means whereby the speeds of the respective secondary shafts are compared with the speed of the master shaft 20M, and such detecting means include a plurality of commutator switches MS, SI, S2, S3 and Sn associated respectively with the shafts 20M, 2li-I, 202, 20-3 and 20-N. Each such commutator switch includes a circularly arranged series of commutator bars 36 and one or more brushes adapted for cooperation with such commutator bars 36. As shown in Fig. 1 the commutator bars 36 constitute the stationary parts of the switches, while the rotating parts of the switches are afforded by the brushes thereof, and hence the brushes of the respective commutator switches are arranged to be driven by the shafts with which their commutator switches are associated. Thus the master commutator MS has a single brush 40 driven by the shaft 20M, while the commutator switch SI has three angularly spaced brushes 4l, 42 and 43 driven as a unit from the secondary shaft 2-|. Each commutator switch S2, S3 and Sn including wires 45, 46 and 41 which are extended respectively from the brushes 4I, 42 and 43 through conventionalslip ring and plug connections and selected commutator segments of each secondary switch are so connected with different selected segments of the master commutator MS that when the speed of a secondary shaft varies so as to cause relative rotation to exist between that shaft and the master shaft 20M, circuits will be established to the wires 45, 46 and 41 in a sequence which depends upon the sense of such relative rotation and at a frequency dependent upon the magnitude of such relative rotation. In atta-ining this result the successive commutator bars 36 of the master commutator MS are allocated in succession to the respective secondary commutator switches and are electrically connected to correspondingly positioned commutator bars of the secondary commutator switch to which they are allocated. Where the master commutator switch is to be associated with four secondary commutator switches, as in the form shown in Fig. 1 of the drawings, the master commutator bars 36 may be considered as being divided into successive groups each including four commutator bars, and the connections for one such group are shown in detail in Fig. i. Thus, the upper bar 36 just to the right of the vertical center line of the master commutator MS may be considered as the rst'one of such a group, and a wire 5l connects this bar to the correspondingly positioned commutator bar of the commutator switch Si. The second bar of such a group, that is next bar 36 of the master commutator MS, in a clockwise direction, is connected by a wire 52 .to the correspondingly positioned bar of the commutator switch S2; while the third and fourth bars of the group are connected by Wires 53 and 54 to corresponding commutator bars of the switches S3 and Sn respectively. In the present instance each annular series of commutator bars is so arranged that each bar 36 is electrically connected to the diametrically opposite commutator bar, as by wires 55, so that where each commutator contains but forty-eight bars, as in the present case, master commutator contains but six groups of bars of four bars each which must be connected in the manner hereinabove described. Thus, the first bar 36 of the next group has a wire 5I extended therefrom to the corresponding segment of the switch SI; so that in the switch SI three dead or unused commutator bars are disposed between those bars which are connected to the wires 4I and 5I. The other connections between the master commutator and the respective secondary commutatcrs are made in-the manner described so that, within of the circumference of each secondary commutator, six equally spaced commutator segments are connected to correspondingly positioned bars of the master commutator.

Where diametrically opposite commutator bars are electrically interconnected as in the embodiment shown in Fig. 1, the brushes 4I, 42 and 43 of each secondary commutator switch as Si are arranged so as to lie entirely within 180 of the circumference of the commutator. This assures completion of the circuits to the wires 45, 46 and 41 in the desired manner, and avoids false indications of relative rotation or sense of such relative rotation.

To provide for such completion of electrical i circuits through the respective brushes 4|, 42 and 43 and the master brush 40, a ground connection 56 is provided from the master brush 40, and the wires 45, 46 and 41 from the respective secondary commutator switches are extended to the related control-units as CUI. Since all of these control units in Fig. 1 are of similar construction, the specific description of such construction and of the relationship to the secondary commutator switches and to the controlled mechanism will be coniined to the control unit CUI. Thus, the control unit CUI includes a pair of balanced relays 60 and 10, the relay 60 having a pair of actuating coils 6I and 82 adapted to act upon opposite ends of a balanced armature is centrally pivoted at 64 in symmetrical relation with respect to the two coils 6| and 62. The armature 63. is yieldingly urged toward the neutrai position shown in Fig. 1, and this is accomplished in the present instance by a pair of normally aligned spring members 65 and 66 which are anchored at their remote ends at 65 and 66'. At its other end the spring member 65 acts through an insulating member 61 to urge the adjacent end of the armature 63 downwardly toward the actuating coil 62, while the other end of the spring member 66 acts in a similar manner through an insulating member 68 tourge the other end of the armature 63 downwardly toward the actuating coil 6|. Thus the two opposed or balanced springs 65 and 66 tend to maintain the armature 63 in its neutral position as shown in Fig. 1.

In the present instance the spring member 65 serves also as a relay contact which is normally separated from an opposing contact 69, but when the relay coil 6| is energized, the armature is rocked in a. counterclockwise direction so as to elevate the right hand end of the armature and thereby engage the contacts 65 and 69.

'The other balanced relay 10 is of generally similar construction in that it has two actuating coils 1| and 12 arranged to act on opposite ends of an armature I3 which is centrally pivoted at 14. Similar springs 15 and 16 act through insulating members 11 and 18 respectively to urge the opposite ends of the armature 13 downwardly, thereby to impart the desired balanced characteristics to the armature. 13. In the relay 10, however, a plurality of relay contacts are associated with each of the insulating members 11 and 18. Thus, on the right hand side of the relay 'i0 a switch pile is provided wherein the spring member 15 constitutes one of three movable switch or relay contacts of similar form. Thus two additional spring contacts 80 and 8| are associated withthe insulating member 11 for upward actuation thereby when the armature is actuated in a counterclockwise direction. Stationary relay contacts 82, 83 and 84 of the spring type are disposed respectively above the movable contacts 15, 80 and 6| in normally spaced relation thereto, while a similar stationary relay contact 85 is disposed beneath the movable contact 80 in a normally engaged relation thereto, so that when the relay coil 1| is energized so as to raise the right hand e'nd of the armature 13, the circuit through relay contacts 85 is opened, and circuits through the relay contact 82, 83 and 8 4 are closed. 1

On the left hand side of the relay 'I0 a simi- 63 which the contact 95 by a wire larly arranged switchpiie is associated with the insulating member 18, to thereby provide movable contacts 90 and 9| connected to the insulating member 18. Stationary relay contacts 92, 93 and 94 of the spring type are disposed respectively above and in normally spaced relation to the movable relay contacts 16, 90 and 9|, while a similar stationary relay contact 95 is disposed beneath and in normally engaged relation tothe movable relay contact 90. Thus when the left hand end of the armature 13 is elevated due to energizaton of the actuating coil 12, the circuit through relay contact 95 is broken, and circuitsare-established through the relay contacts- 92, 93 and 94. Y

The energizing circuit for the relay coil 6| is extended from the brush 4| of the related secondary commutator switch, vas Sl, by the wire which is connected to one end of the coil 6|, and this circuit is continued from the other end of the coll 6| by a wire 96 which extends to the relay contact 85. The relayv contact 85 normally engages the contact 80 which is connected to 91; and thus the circuit is normally extended to the contact 90 which is connected by awire 98 to one terminal of a source of electrical energy such as a battery 99. The other terminal of the battery 99 is grounded at |00, thereby to complete the energizing circuit for the relay coil 6|.

The relay coil 6| of the present embodiment of the invention constitutes the master relay coil ofthe control unit, and for reasons which will become apparent as the description proceeds, this relay coil 6| is arranged to possess slow-to-release characteristics so as to remain energized, and normally maintain the relay contacts -69 closed, for a predetermined period after momentary energization of the relay coil 6|. Such slowto-release characteristics in the relay coil 6| may be attained in different ways, but as herein shown, a condenser |0| is connected across the terminals of the coil 6| to attain this result.

Ordinarily, by selection of the proper value for the condenser |0I, the desired normal release period may be attained within reasonable limits of accuracy, but to simplify attainment of the desired accuracy of the release period, an adjustable resistance |02 may be connected across the terminals of the coil 6| in parallel with the condenser |0|.

The energizing circuits for the actuating coils 1| and 12 are arranged to include the relay contacts 65 and 69 so that neither of these two relay coils may be energized except during an operative period of the mmter relay coil 6| and to accomplish this, wires |04 and |05 are extended respectively from one terminal of each of the coils 1| and 12 to one end of a wire |06 which is connected at its other end to the relay contact 65. The other terminal of the relay coil 1I is connected to the wire'41 by a wire |01 while the other terminal of the relay coil 12 is connected to the wire 46 by a wire |08 thereby to aiord circuits through which the relay coils 1i or 12 may be selectivelyv energized during periods when the contacts 65-69 are closed.

When the relay coil 1| is thus energized, a holding circuit is established therefor, so as to thereafter render the coil 1| independent of the continued completion of a circuit through the brush 43, a wire |09 being extended from the wire |01 to the contact 15, and the contact 82 being connected by la, wire l I0 to ground at I l. Thus when energization of the relay coil 1| operates to raise the right hand end of the armature 13, the relay contacts 15 and 82 are engaged, and the desired holding circuit for the relay coil 1I is established. This holding circuit, of course, includes the relay contacts 65-$9, so that the holding circuit is broken when thegarmature 63 of the relay 60 returns toits normal position. A similar holding circuit for the relay coil 12 is afforded by a wire I I2 extended from the wire 46 to the relay contact 16 and a wire I I3 extended from the relay contact 92 to ground at II4. Hence it will be clear that when the relay coil 1I or the relay coil 12 has been energized during the delay period of the relay coil 6I, the establishment of the holding circuit for the one of the coils 1I or 12 which has been energized results in this particular coil remaining energized until the master relay contacts 65-69 are opened. It will be observed, of course, that during such period the other coil, as 1| or 12, may be energized, but this does not shift or return the armature 13 or change the condition or relationship of the contacts of the relay 10 so long as the holding circuit remains closed; and such energization cannot take place after the holding circuit of the previously energized coil of the relay 10 has been broken by separation of the contacts 65-59. Such functioning of the apparatus is due to the functional characteristics of the balanced relay 10,-for it will be evident that where prior energization of one of the actuating coils has shifted one end of the armature 13 toward the energized coil, this'energized coil will continue to exert an attractive force on the armature which will be substantially greater than the attractive force which could be exerted by the other coil in the event it were energized under such conditions.

The manner in which the relay coils of the control unit, as CUI, are energized is thus dependent to the relative positions of the secondary shaft and the master shaft as well as upon the sense and rate of any relative rotational movement which exists therebetween; and the selective positioning of the armature 13 in one actuated position or the other is indicative of the sense of relative rotation which exists between the master and secondary shaft. Hence the condition of the relay 10 is utilized to control the speed governing mechanism 26, and to this end the normally open contacts 83 and 93 of opposite sides of the relay 10 are placed in control of the actuating means such as the motor 21 or the solenoid 30 so as to govern the operation or adjustment of the speed control means in opposite directions. Of these two contacts, the contact 93 is closed when the sense of relative rotation of the shafts indicates that the speed'of the secondary shaft is to be reduced, while the contact 83 is closed when the sense of relative rotation indicates that the speed of the secondary sha-ft is to be increased; and therefore the contact 83 is connected by a wire II1to one terminal of that field winding of the reversible motor 21 which will drive the motor in such a direction -as to increase the fuel supply to the engine 22, it being observed that the common terminal of the two field windings of the motor is grounded as at H6. Thus, closure of the contact 83, when the relay coil 1I is energized, completes a field circuit for the motor from ground at through the battery 99, the wire 98, relay contacts 95 and 9i?, the wire 91, relay contacts 80 and 83, the wire l il?, and through the proper one of the eld coils of the motor 21 back to ground at IIS. The circuit from the contact 93 to the other terminal of the other field winding of the v tively to motor 21 is afforded by a wire II5, so that when the relay contact 93 is engaged by the movable contact 90, an energizing circuit is established to vthe proper field winding of the motor to reduce the speed of the engine 22.

In the event that the speed governing means is hydraulically actuated, as by means of the hydraulic actuator or motor 29, the control valve thereof is shifted in opposite directions selectively by the two-way solenoid 30; and when such structure is to be used the common terminal of the solenoid 30 is grounded as at II8, and the other ends of the solenoid coils are connected respecthe Wires II1 and I I5, as indicated by dotted lines in Fig. 1, so as to cause appropriate valve movement when the control circuits are selectively closed through the contact 83 or contact 93. A

As an example of the operation of the structure thus far described it will be assumed that both the master shaft 20M and the secondary shaft 20-I are rotating ina clockwise direction, as indicated by the arrows in Fig. 1, and that the speed of the secondary shaft 20-I is slightly greater than that of the master shaft so that the sense of rotation of the secondary shaft is clockwise relative to the master shaft. For descriptive purposes, therefore, the master shaft may be considered as being stationary, with the brush 40 in the position shown, while the secondary shaft 20--I and the connected brushes are rotating in a clockwise direction. Under such circumstances, the rotation of the brush assembly of the secondary commutator switch will establish a circuit from ground at 56 through the brush 40, the wire 5I and the commutator bars connected thereby, the brush 4I, the Wire 45, the relay coil 6I, the wire 96, relay contacts 85 and 80, the wire 91, relay contacts and 90, the wire 98, and through the battery 99 back to ground at |00. Thus the master relay coil 6| is energized and the armature 63 is rocked in a counterclockwise direction so as to close the relay contacts 65-69. Such energization of the master relay coil 6I continues until the aforesaid circuit is broken, as by the brush 4| passing in a clockwise direction past and out of contact with the commutator bar connected to the wire 5I, for during this period of energization the condenser IIII is charged so a-s to maintain the coil 6I' energized and the relay contacts 65-69 closed for the desired delay or release period. Thus during such delay period, the continued closure of the contacts 65-69 conditions the common circuit to the relay coils 1I and 12 so that these relay coils may be selectively energized by the cooperative action of the commutator switches MS and Sl.

It may happen, of course, that the speed of relative rotation of the shafts 20M and 2li-I is so slow that the relay coil 6I will become ineffective and the relay contacts 65-69 will be opened prior to the closure of a circuit to one of the secondary relays 1I or 12. Such operation indicates that relative speed of the two shafts is within the allowable tolerance. However, if the speed of relative rotation of the two shafts exceeds such tolerance, and if it is of such a sense that the secondary shaft 20-I is rotating in a clockwise direction relative to the master shaft 20M, the brush 42 of the secondary commutator will move into contact with the commutator bar which is connected to the wire 5I prior tothe expiration of the release period of the master relay coil 6I, and hence the circuit to the secondary relay coil 12 will be energized. This establishes a circuit through the contacts 90-93 and the wire .I l1 to that winding of the motor 21 which will operate the speed governing means 26 to reduce the speed of the engine 22.

In accordance with the present invention, the

l amount or extent of the corrective adjustment is varied and controlled in various was so as to attain unusual accuracy of correlation and unusual stability and the minimum fluctuation in the speed relationship of the two shafts. Thus, as one factor is attaining such controlled extent of the corrective adjustment, it will be clear that the length of the unexpired portion of the delay period ofthe master relay coil 6| at the time when the secondary relay coil, as 12, is energized constitutes a variable quantity which is in a general way a measure of the amount of corrective adjustment which is needed to re-establish the desired speed relationship. It has been pointed out, however, in the preceding discussion that in attaining speed correlation within a relatively ysmall tolerance, in the order of one revolution per minute, the mechanism must be able to detect extremely small speed differences, and this requires that the release period of the master relay 6| be quite extended in most instances. Thus, under many circumstances the extended release period would tend to so extend the operative period of the adjusting motor 21 as to cause over-correction of the speed of the secondary shaft. Under the present invention, however, means are provided which enable a release period of the desired length to be employed for the master relay coil 6| without danger of objectionable over-correction. In the embodiment of the invention shown in Fig. 1 such means include the coil 62 of the balanced relay 60, and this coil 62 utilized as means for reducing the release time of the relay coil 6| whenever a control operation of the speed adjusting motor 21 is instituted. Thus, a normally long release period in the order of three or four seconds may be employed for the master relay coil 6|, thereby to enable extremely small speed differences to be detected, and yet, this may be accomplished without causing an undue amount of corrective adjustment to be applied to the secondary shaft. Where the relay coil 62 is employed as a part of the means for accomplishing this result, circuits are provided for the relay coil 62 which are closed whenever one of the secondary relay coils 1|' or 12 is operative to close the related relay contacts. Thus the relay contact 8| is connected by a wire |20 to ground at and a wire |2| is extended from the relay contact 84 to one terminal of the relay coil 62. A Wire |22 from the other terminal of the relay coil 62 is connected to the wire 98, thereby to extend circuit through the battery 99 and back to ground at |06. Hence when'the relay coil 1| causes the contacts 8|-84 to be closed, the relay 62 is energized. Similarly, the contact 9| is connected to ground at H4 by a wire |23, and the relay contact 94 is connected to the wire |2| by a wire |24, so that upon closure of the relay contacts 9|-94, the relay coil 62 will also be energized.

When the relay coil 62 is thus energized, it attracts the right hand end of the armature 63 With a force which opposes the action of the coil 6| and augments the resilient forces which tend constantly to restore the armature to its neutral position, and hence as the energy of the condenser is gradually dissipated through the coil 6|, the combined action of the coll 62 and the resilient return forces acting on the armature 63 will restore the armature to its normal position more quickly than if the coil 62 were not energized. The effectiveness of the coil 62 is reducing the release time of the coil 6| is of course dependent upon the intensity with which coil 62 is energized. This intensity may be governed and matched with the characteristics of the relay coil 6| by means such as a resistance |25 included in the wire |22 so as to limit and reduce the current flow in the relay coil 62.

In accordance with the present invention the effectiveness of the relay coil 62 in reducing the release time of the master relay coil 6| is also governed differently in accordance with the direction of the corrective adjustment which is to be made, for by so doing, the effectiveness of the speed adjustments in different directions may be correlated despite the fact that the load on the secondary shaft tends to accelerate the corrective action when the speed of the secondary shaft is being reduced, and tends to retard the corrective action when the speed of the secondary shaft is being increased. Thus, the wire |24 includes another resistor |26, while the wire |2| includes resistance afforded for illustrative purposes by two resistors |21 and |28 in series, and the total resistive value -of the resistors |21 and |28 is materially greater than the value of the resistor |26. Such resistors |21 and |28 therefore serve to reduce the current `iiow to the relay coil 62, below the value of the current which may fiow through the circuit which includes the resistor |26, and hence when the corrective speed adjustment is to increase the speed of the secondary shaft, the relay coil 62 will be less effective and the period of corrective speed adjustment is greater than when the speed adjustment is to reduce the speed yof the secondary shaft. 'In attaining such difierent reduction of the release period of the relay coil 6| in accordance with the direction in which the corrective adjustment is being made, a, common resistance |25 has been shown in Fig. 1, resistances of different values have been shown in the branch leads to the relay contacts 84 and 94, but it will be recognized that in many instances the common resistance |25 and the resistor |26 might be eliminated and the desired differential in the release period of the relay coil 6| might in such a case be attained solely by resistance, as |21 or |28, in the'circuit to the relay contact 84.

It will be observed that each of the relay coils 1| and 12 is illustrated as having an individual condenser |29 connected across its terminals, and in many instances such .condensers may be of relatively small value or capacity so as to act merely to facilitate operation of such coils on current of a pulsating character. However, in most instances the condensers |29 are made of such a value as to impart at very slight slow-torelease period to the relay coils 1| and 12, for by so doing, the control apparatus may be caused to impart a relatively small corrective speed adjustment to the secondary shaft even through the detected speed difference is so slight that the energization of the coil 1| or 12 take place at substantially the end of the normal release period of the master relay coil 6|.

In Fig. 2 of the drawings the invention is illustrated as embodied in a control unit CUIA which under some conditions may be advantageously substituted for each of the control units illustrated in Fig. 1 so as to attain accurate correlation of the secondary shafts with the master shaft. The control unit CUIA is in many respects similar to the control unit CUI, but the control unit CUIA includes an additional baloperation of the balanced relay A in the control anced relay which is associated with and conunit CU IA serves to govern the operation of the trolled by the other two balanced relays. Those balanced relay |30, and this relay is, in turn, elements of the control unit CUIA which correarranged to control the energizing circuit to a spond in form and function to elements included 5 related adjusting unit, as 35| shown in Fig. 1.

in the control unit CUI have been identified by In accomplishing this result, the balanced relay corresponding reference numerals with the suffix |30 has a movable contact |31 arranged when the A added in each instance. Thus the control actuating coil |3| is energized to engage a staunit CUIA includes a balanced relay 60A having tionary relay contact |38, and the relay contact actuating coils SIA-and 62A arranged to operate lo |38 is connected to the wire ||1 which extends t upon opposite ends of a balanced armature 63A to the related speed adjusting unit in the manner One terminal of the relay -coil GIA is connected disclosed in Fig. 1. Similarly the' balanced relay to the wire which may extend from one of the |30 has a movable contact |39 arranged to be ,t secondary commutatorswitches, as SI, and the actuated upwardly when the coil 32 is energized,

differently positioned in Fig. 2 than the correcontrol unit shown ln circuit from the other terminal of the relay coil 15 and in such upward movement the contact |39 BIA is extended to the relaycontact 85A by a is engaged with a contact |40 which is conwire 96A. It will be observed that the balanced nected with the control wire ||5 in the manner relay 10A has fewer contacts than the balanced disclosed in Fig. 1. Thus, as aresult of the operrelay 70, fOl the Contacts 8|, 84, 9| and 84 are ation of the relay 10A, the actuating coils of the not included in the relay 10A, the functions of 2o balanced relay |30 are selectively energized so as such omitted contacts being transferred in the to cause circuit closure to the speed adjusting present instance to the balanced relay 30. It unit in the proper manner.A

will be observed that while the battery 99A is It wlll be recalled in the embodiment of the Fig. 1 of the drawings, the arranged to have a normal derable magnitude, thereby sponding battery 99 in Fig. 1, the connections to 25 master relay e011 was the -relays A and 10A are in fact the same in release time of consi Flg- 2 to impart initial sensitivity to the control appa- The Wires 45 and ll shown in Flg- 2 may be ratus, and provision was made for reduction of extended from a secondary commutator switch the release period el' the master relay e011 es an ln bhe manuel illustrated iu Flg- 1 and these 30 incident to the initiation of a control operation. wires are connected to the relay coils 1|A and provision is also modo 1n the control unit of Fig 72A ln lie same manner as 1in Flg 1 Thus, When 2 for the attainment of such operation, and for circuit 1s extended to the wire 45 by thecommuthis purpose the balanced relay |3|) has a movtator devices, the relay coil SIA is energized and able relay Contact |4| which is actuated, when the relay Contacts 55A59A are Closed- The re- 35 the coil |3| thereof is energized so as to engage lay Coil SA has the reSiStanCe '02A and the C011- a stationary relay contact |42. On the other side denser |0|A connected across its terminals and of the relay |30 a statlonary Contact |43 is pretherefore has slow-to-release characteristics, and vided Wlrleh ls engaged with a Contact 44 when hence the relay coil SIA remains effective after the cell |3201e the relay |30 is energized. The the energizing circuit thereto has been broken. 40 two control switches which are thus allorded in In the eventthat the rate of relative rotation of the relay |30 are utilized to control and reduce the master and secondary shafts is sufficiently the release tlme 0f' the master relay SIA when great, the circuit to the wire 46, or to the wire 41, t the relay |30 is actuated Thus a'wlre |45 is Will be completed prior to the expiration -of the extended from the Contact |42, and a wire |46 release DeI'iOd 0f the relay C011 SA, 2md the 1`e 45 is extended from the contact |44 and these wires lated secondary coil, as the coil 1|A, will therefore be energized. In such an instan-ce the righthand end of the armature 13A would be elevated, thereby to establish a holding circuit for the relay Poll 'llA through contacts 7'5A 32A Thls 50 circuit from ground at |50 and through the relay holding circuit includes the contacts SSA-69A so oon 52A has two branches to the two relay eenthat the holding circuit will be broken when the toets |42 and |44 and this Circuit may be oom y pleted selectively through the contacts |42 and Such actuation of the armature 13A also serves |44 so as to extend circuit to and through the to separate the contact A from the contact 55 battery 99A and boek to ground at |00A For A, thereby to breali the circuit to the master this purpose o Wire |5| is extended from the eenrelay SA and make 1t impossible to again enertact |4|, and a wire |52 is extended from the gize this relay coil until the armature 13A has re- Contact |43, these two wires being joined at a turned lSOlS r1eullellpasition. terminal |53 from which a wire |54 is extended When the relay contact 80A is thus elevated it 60 to the ungrounded side of the battery 99A. iS engaged With the contact 83A, thereby to ex- It will be recalled that the eilectiveness of the tend eireuit through a Wire 35 t0 011e terminal relay coil 62A in reducing the release time of the of the actuating coil |3| of the balanced relay relay coil SIA is governed by the amount of cur- |30. When the other one of the coils of the relay rent which flows through the coil 62A when this 10A is energized, the left-hand end of the arma- 65 coil is energized. Thus resistors |55 and |56 are ture 13A is elevated, and a holding circuit is esincluded in the wires |45 and |46, respectively, to tablished through the contacts '16A and ZA. At control current flow through the relay coil 62A. the Same time the Separation of the contact SliA 'In order that the release time of the master relay from the contact 95A breaks the energizing cir- MA may be reduced in different amounts in accuit of the master relay coil EIA. The relay con- 7o corclance with the direction in which the correc- Atact A is at this time engaged with the contact tive adjustment is being made. The resistance 83A which is connected by a wire |36 to one ter- |55 is made somewhat larger than resistance |56, minal of the actuating coil |32 of the balanced and hence when the relay coil |3| is energized relay |30. The other terminals of the relay coils so as to cause the speed adjusting apparatus to |3| and 32 are grounded at |34, and thus the 75 increase the speed of the secondary shaft, the

|48 is extended to one terminal of the relay coil 62A. A wire |49 extends from the other terminal of the relay coil 62A to ground at |50. Thus a are joined at a terminal |41 from which a wire unnecessary, and the desired diierence in the period of operationmay be attained solely throughvthe use of the resistance |55 in the wire |45.

The use of the balanced relay |30 in the control unit CU|A is advantageous in that it enables relatively large amounts of current to be drawn through the contacts |38 and |40 independently of the contacts of the balanced relay 10A, and hence the responsiveness of the relay 10A is maintained at a high level at all times. The use of the balanced relay |30 also enables other advantageous improvements to be attained in the operation of the control unit, for the relay coils |3| and |32 may have condensers |60 connected across their terminals so as to impart slow-toreleasecharacteristics to these relay coils. Through the use of this arrangement the period of operation of the speed adjusting means may be extended to some extent beyond periods of closure of the contacts of relay 10A, and hence when the speed dilerential between the master and secondary shafts is relatively high, the extended operative periods of the relay coils |31 and |32 will bridge the gap between the operations of the relay 10A. This produces substantially continuous operation of the speed adjusting means when the speed differential is relatively high, thereby to restore the desired speed relationship quite rapidly. Such operation of the control unit CU|A is, however, attained in such a manner that the sensitivity of the control unit to relatively small speed differences is not objectionably changed or reduced. Thus it will be clear that where the sloW-to-release characteristics of the coils of the relay |30 extend the operating periods of the speed adjusting means beyond the period of closure' of the contacts of the relay 10A, the relay 10A and the master relay coil GIA will then be free and in proper condition to detect reversal of the direction of relative rotation of the two shafts. In the event that such reversal takes place, the master relay coil 6|A will again Ibe operated and the proper one of the relay coils of the relay 10A will also be operated. This will of course establish an energizing circuit to one of the actuating coils of the relay |30 which will tend to return the armature |33 to its neutral position. Hence the newly energized relay coil oi the relay |30 will act to reduce the release time of the previously actuated one of these coils, and under most circumstances will operate the armature through its neutral posi tion and into its other active position to thereby institute a speed adjusting operation in the opposite direction.

In Fig. 3 of the drawings a control unit CUIB is illustrated wherein the reduction in the normal release time ofthe master relay is attained through the use of a more conventional type of relay means. Thus the control unit CUIB has three relays |60, |6| and |62 arranged for association with a detecting means such as the commutator switch devices of Fig. 1, and adapted to control speed adjusting means in the same manner as the control unit CU of Fig. 1. The relay |60 has but one movable contact |63 which is arranged in a normally spaced relation to a stationary relay contact |64. The relay |6| has four movable contacts |66, |68, |61 and |63, and when the relay |6| is de-encrgized, the relay contact |65 is engaged with a stationary contact |69, the relay contact |66 is opposed to but separated from a stationary contact |10, the relay contact |61 is engaged with a stationary contact |1| and is in a position to be separated from the stationary contact |1| and engaged with a contact |12 when the relay |6| is energized, while the relay contact |66 is disposed in spaced but opposed relation to a stationary relay contact |13 when the relay |6| is energized.

The relay |62 has contacts of the same character and arrangement as the relay |6|, there being four movable contacts |15, |16, |11 and |18. The relay contact |15 is arranged to normally engage a stationary relay contact |19, while the contact |16 is normally spaced from a stationary relay contact |80 so as to be engageable therewith when the relay |62 is energized. The contact |11 is disposed between stationary relay contacts |8| and |82 so as to normally engage the contact I8 while the relay contact |18 is disposed in normally spaced relation to a contact |83 so as to be engageable therewith when the relay |62 is energized.

In associating the control unit CUIB with a detecting means such as the commutator switches shown in Fig. 1, the wire 65 is connected to one terminal of the relay |60 which constitutes the master relay of the control unit CUIB, and circ-uit is extended from the other terminal of the relay |60 by a wire |85 to the relay contact |8| of the relay |62. This relay contact is at this time engaged With the contact |11 which is connected by a wire |86 to the contact |1I of the relay |6|, so that circuit is thereby extended to the contact |61. A wire |81 connects the contact |61 to one side of an energy source such as a battery |86, and the other side of the battery |88 is grounded at |89 to thereby complete an energizing circuit for the master relay |60. The relay has the desired slow-torelease characteristics imparted thereto by means such as a condenser |9| connected in parallel across the terminals of the relay, a resistance |90 being connected in parallel with the condenser |9|, and hence the relay contacts |63|84 are maintained closed for a predetermined normal release period after the opening of the energizing circuit of the relay |60.

The energizing circuits for the relays |6| and |62 are arranged to include the contacts i63| 64,

y thereby to render operation of such secondary relays dependent upon operation of the master relay |60. Thus a battery has one terminal grounded as at |96 While the other terminal thereof is connected by a wire |91 to the relay contact |63, and the contact |64 has a wire |98 extended therefrom to a terminal |99. Branch lead wires 200 and 20| are extended from the terminal |99 to corresponding terminals of the relays |6| and |62 respectively. The other terminal of the relay |6| is connected by a wire 202 of the relay contact |15 of the relay |62, which normally engages the contact |10 to which the wire 46 is connected, so that when the detecting means, such as the commutator switches of Fig. 1, extends circuit from ground and through the wire 4 6 during the operating period of the master relay |60, the relay |6| is energized. When this occurs, a holding circuit for the relay |6| is established, the contact |10 being grounded at 203, and the contact |66 being connected to the wire 202 by a Wire 204. This holding circuit extends from ground 203 through engaged contacts |10 and |66, the wires 204 and 202, the relay coil |6|, wires 200 and |98, the contacts' |64|63 and through the battery |95 to ground. Similar circuits are provided for energizing the relay |62, the wire 41 being connected to the contact |65 so as to extend circuit to contact |69 and thence through a wire 205 to the other side of the relay coil |62. The desired holding circuit is in this instance ail'orded by grounding the contact |80 at 206 and connecting the contact |16 to the wire 205 byawire 201.

Thus, in the control unit CUIB the secondary relays |6| and |62 cannot be energized unless the circuit to a respective one of these two relays is completed through the wire 46 or the wire 41 at a time when the relay contacts |63|64 are closed, and when one of the relays |6| or |62 has been thus energized it not only completes its own holding circuit through the contact |66 or |16, but also, through opening ofthe contact |65 or |15, breaks the energizing circuit to the other one of the secondary relays so as to prevent operation of the other secondary relays during the time when the previously energized secondary relay remains operative. The master relay |60 is, of course, normally operated at least once in each relative rotation of the compared shafts, and ii such relative rotation exceeds the allowable rate or tolerance, the circuit to one of the secondary relays will be completed prior to the expiration of the release period of the master relay. Thus, in accordance with the sense of the detected variance, the relay |6| or |62 will be operated, and when the relay 6| is operated the circuit from the battery |88 will be extended to the relay contact |12 which is connected to the wire of a speed adjusting unit such as the unit 35| of Fig. 1. Similarly the relay Contact |82 is connected to the wire ||1 of the speed adjusting unit, so that when the relay |62 is energized, the speed adjusting unit will operate in the other direction.

In the control unit CUIB, as in the control unit CUI', the normal release time of the master relay may be made relatively long, thereby to attain high sensitivity to small differences of speed, and means is provided for reducing this normal release time of the master relay as an incident to the initiation of a control operation. In attaining this end wire 2|0 is extended from one terminal of the relay |60 to a terminal 2|| from which branch leads 2|'2 and 2|3 extend to the contacts |13 and |83 respectively. A wire 2|4 is extended from the other terminal of the relay |60 to a terminal 2|5, and a wire 2I6 which includes a resistor 2|1 is extended from this terminal to the relay Contact |18. A resistor 2|8 is connected between the terminal 2 5 and the relay contact |68, and hence when the secondary relay |6| is operated, an alternative or shunt circuit, the effectiveness of which is controlled by the resistor 2 |`8, will be connected across the condenser |9| -to thereby reduce the release time of the master relay 60. A conductor 2 6 leads from the terminal 2|5 to one end of a resistor 2|1, the other end of this resistor being connected to relay contact |18. Hence when relay |62 is energized an alternative or shunt circuit is connected across the condenser |9| and in this in- 18 stance the effectiveness of this shunt circuit is controlled by the resistor 2|1. As in the case of the c ontrol unit CUI. it will be evident that in some instances it may be desirable to reduce the release time of the master relay in different amounts in accordance with the direction in which the corrective adjustment is to be made, and hence the resistanceV 2 I8, which become.: ef-

fective when the speed of the secondary shaft is being reduced, is made somewhat smaller than the resistance 2|1, thereby to cause the release time of the master relay |60 to be reduced in greater amount when the speed of the secondary shaft is being reduced than when such speed is being increased. This result will be realized since the resistance 2 |8, being smaller than the resistance 2 |1, will enable the charge in the condenser |9| to be dissipated more rapidly than such charge will be dissipated when the resistance 2 |'1 is included in the shunt circuit about the condenser |9|. Thus, while attaining great sensitivity to small speed differences, the control unit CUIB is operable to apply corrective adjustment to the secondary shaft without objectionable over-correction, and hence the relative speed of the compared shafts may be maintained within an extremely small tolerance through the use of the control unit CUI B.

In Fig. 4 of the drawings the invention has been illustrated as embodied in a control unit CUIC which is adapted to be used in a control apparatus such as that shown in Fig. 1, and in this control unit the master relay and the secondary relays are of the form utilized in the control unit CUIB and these relays are associated with a balanced relay |30C so that the control unit CUIC attains the same desirable operating characteristics as the control unit CUIA. Thus in the control unit CUIC master and secondary relays correspond in most respects to the relays of the control unit CUlB, and hence the same reference characters are employed with the suix C added in each instance. The relays |6|C and |62C, however, have but three movable contacts, the contacts |68, |13, |18 and |83 having been eliminated, and the function of these relay contacts in reducing the release time of the master relay has been transferred to the balanced relay |300. Moreover, the relay Contact |820 is, in this embodiment of the invention, connected by a wire |350 to one terminal of the relay coil |3|C, so that when the relay |62C is operated, circuit is closed to the relaycoil |3|C so as to close the contacts |31C-I38C and thereby extend circuit from the battery |C to the speed adjusting unit through the wire ||1. Similarly, the contact |12C is connected by a Wire |36C to one terminal of the relay coil |32C, thus to cause the contacts |39C|40C to be closed when the relay |62C is operated. This closes a circuit to the speed adjusting unit through the wire |'5. Thus the speed 4adjusting unit will operate in opposite directions in accordance with the manner in which the secondary relays |6|C and |62C are operated. In this embodiment of the invention the two wires 2|0C and 2|4C from opposite terminals of the master relay |60C are extended to terminals 2| IC and 2|5C respectively, as in the embodiment of Fig, 3; and branch leads 2| 2C and 2|3C are extended from the terminal 2| IC to the relay contacts |430 and |4|C, respectively. A resistor 2|1C is connected, by means including a wire 2| 6C, between the terminal 2|'5C and the relay contact |420, while a somewhat larger resistance 2|8C is connected between the terminal 2 5C and control unit CUIA,

the relay contact I44C. Hence, when operation of the relay ISUC in one direction or the other initiates operation of the speed adjusting means, a circuit through `the resistance 2I1C or 2l8C is established which causes the release the master relay IBUC to be reduced. The extent of such shortening of the release period of the master relay may be dierent in diiferent directions of operation of the relay 130C, as by using different values for the resistors 2|1C and 2I8C.

The relay ISllC in the control unit CU IC, as in may have a short sustained period of operation, as will be imparted thereto by condensers IBDC of substantial capacity, and by such a sustainedperiod of operation the speed adjusting operation, in some instances where the speed diiferential is high, may be continuous so as to correct the objectionable speed diilerence more quickly. Moreover, such an extended operating period for the relay ISOC may be safely used because upon detection of reversal of the sense of rotation of the compared shafts, the other relay coil of the relay ISUC is energized so asv to cause prompt reversal of the relay HUC and prompt initiation of the desired speed correction in the opposite direction.

As hereinbefore pointed out, it is usually desirable,-when the detected variance from the desired speed relationship between two shafts is unusually large, to re-establish the desired relationship as rapidly as possible. and in other embodiments of the invention, as for example, in those embodiments shown in. Figs. 2 and 4, the speed adius'ting mechanism is operated continuously when the speed differential is large, thereby to reduce the time necessary to re-establish the desired speed relationship. Under circumstances where such mechanism does not operate sumciently fast. the means illustrated in Fig. 5 may be employed, and it will .be observed that this means is there illustrated in association with a control unit CU which may constitute a control unit constructed-in the same manner as any one of the control units CUI, CUiA, CUIB or CU IC. Thus, as shown in Fig. 5, the wires H5 and lil are connected to the respective eld winding of an actuating motor 21D which operates the controlled speed governing mechanism 26D, and the common terminal of such field windings is connected to ground at HSD through a resistor 220 which normally limits the voltage and current applied to the motor 21D to thereby normally govern the speed of the motor. A shunt circuit 22| including a normally open contact 222 is' provided around the resistance 220 so that when the contact is closed, the resistance 220 will be shunted out of the motor circuit and the motor will therefore operate at a higher speed in accomplishing the desired speed adjusting operation. In accordance with this invention such closure of the contact 22 is automatically accomplished when the detected speed differential is large, and this is done .by providing the contact 222 as a part of a relay 222 having similar actuating coils 224 and 225. either one of which will effect closure of thecontact 222. Corresponding terminals of the relay coils 224 and 225 are grounded at 221, while the other terminals of the coils 224 and 225 are connected respectively by wires 228 and 229 to the wires lli and Ill. The relay coils 224 and 225 are of the slow-to-operate type, and are so arranged that when the control impulses passing through the wire H1 or IIE are relatively short, as Iwould be Period ofv in the event that the speed diderential is rela,-

l IIB or lll become quite long, a condition which indicates a relatively high speed dierential, the relay 22a operates and the contact 222 is closed so as to cause operation of the speed adjusting means at a higher speed. Thus, the speed adjustment will be accomplished more rapidly, and as the desired speed relationship is approached, the length of the control impulses in the wire I I5 or the wire I I1 will decrease and the relay 223 will release, thereby to cause the final -speed" adjustments to be made more slowly. lSuch operation of the control means of Fig. 5 thus insures prompt or rapid correction of larger speed differentials while enabling accurate correction of smaller speed differentials, and hence the performance characteristics of the control apparatus as a whole are improved.

It has been mentioned hereinbefore that load conditions on a secondary shaft may render the driving means of such shaft more quickly responsive to reduction of speed than to increase of speed, and while compensation for such difference in responsiveness may in many instances be attained inthe manner taught in connection with the embodiments shown in Figs. 1 to 4, the difference in such responsiveness may in some instances require an even more pronounced difference in the speed adjustments applied to the shaft driving means in opposite directions. Thus the adjusting motor, as 2, may be connected or arranged so as to operate faster in one direction than in the other, and in Fig.. 6 of the drawings an embodiment of the invention is illustrated wherein such operation is attained. As shown in Fig. 6, the adjusting motor 21F has the common terminal of its field windings grounded at HBF, while the other terminals of the two windings are connected by wires HBF and IIIF to speed controlling mechanism 240 which operatively associates the wires HBF and II'IF with the wires IIS and Hl respectively of a control unit CU which may be 0f the kind shown in any one of Figs. 1 to 4. The speed controlling mechanism 240 includes a slow-to-re- 'lease relay 23F having an actuating coil 23|F grounded at one of its terminals at 232F. In the present instance the desired slow-to-release characteristics are imparted to the relay 230F by a condenser 234B' connected across the terminals of the coil 23th', a resistance 2331'1 being connected in parallel with the condenser 234F. The other terminal of the coil 23IF has a wire 235F extended therefrom, and this wire is connected to the energizing circuit of the master relay in such a manner that the circuit to the relay coil 23IF is broken when one of the secondary relays is operated. Thus, as to the embodiment of Fig. l, the wire 2351 is connected to the 'wire 96 so that when one of the secondary relays is operated, the opening of the relay contact or 95 will break the circuit to the relay coil 23411. With this arrangement the relay coil 23R will be continuously energized so long as the speed relationship of the two compared shafts is within the desired range, so as to maintain the movable relay contacts in their upper positions. The relay 23F has two movable relay contacts 24| and 242 which are connected respectively to the wires IIB and H1. The contact 24! is arranged to operate between spaced contacts 243 and 244 which are connected in parallel to the tion it may be observed contact 242 is arranged to operate between spaced contacts 248 and 249 which are connected in parallel to the wire ||`|F by resistances 250 and 25|. The contact arrangement is such that when thc relay coil 23|F is energized, the contact 242 is engaged with the contact 248 and the contact 24| is engaged with the contact 244, and when the relay coil 23 IF is de-energized the contacts 24| and,242 are engaged respectively with the contacts 243 and 249.

It will be recalled that when the speed of the secondary shaft is to be increased, the circuit to the speed adjusting motor, as 21F, is completed through the wire 1, and hence the resistance 250 is made somewhat smaller than the resistance 245, thereby to cause the adjusting motor to operate faster when circuit is extended from the wire Ill than it does when circuit is extended from the wire ||5. Similarly. the resistance 25| is somewhat smaller than the resistance 246, and in addition, the relationship among the resistances 245, 246, 250 and25| is such that the resistance 250 is larger than the resistance 25| and the resistance 245 is larger than the resistance 246. Thus, when the relay 230F is fully energized, as it is when the speed diiferential is relatively small, the Wires I and will be connected to the motor 21E' through the low speed resistances 245 and 250, respectively, and the motor 2'iF will operate at its lower speed in one direction or the other,A as determined by the one of the wires ||5 or which is energized. If the motor 21F is energized for the period which extends beyond the time when the relay 2301 is released, the engagement of the contacts 24| and 242 with the contacts 243 and 249 Iwill throw the other resistances 246 and 25| into association with the wires 5 and ||1 and the speed adjusting operation which is in progress will be completed at a higher speed as determined by the resistance 246 or 25| which is disposed in the energizing circuit of the motor 211i'. In this connecthat the contacts of the relay 23|JF are of the make-before-break type so that operation of the motor 211i1 is not interrupted when a change is made from low to high speed operation. Hence when one of the secondary relays of the control unit operates so as to complete a control or energizing circuit to the motor 21F, the current flow through the motor will be governed by the res istance 245 or 250 so as to cause operation of the motor at slow speed. If the control or adjusting operation of the motor is relatively short, which of course indicates that the amount of variance of the relative speeds of the shafts is small, the relay coil 23|F will remain energized throughout the entire adjustment period. When, however, the period of control or adjustment is relatively long, relay 238F will release so as to close the contacts 243 and 249 and thus cause the motor 211"1 to operate at higher speed for the remainder of the control period. In attaining such action the release period of the relay 2365 is, of course, set at a value which is related to the release time of the master relay of the control unit, such value being substantially less than the maximum release time which the master relay may have during a control operation. Thus, when the control operation of the motor 2`|F continues after release of the master relay of the control unit, that portion of the operating period of the motor 2lF will be at high speed. This desirable operation arises because of the large variance in the relative speed of the two compared shafts, and the operation under such circumstances is further improved by providing a resistance 2365 in series with the condenser 2341i'. This resistance restricts the rate at which the condenser 234F may be charged, and hence when the detected speed differential isl high, and the time between control impulses to the motor 21F is short, the condenser 234F will be charged in a correspondingly less amount. Hence the release time of the relay 2301?' will be reduced under such circumstances and the adjusting motor 21F' will be operated at high speed for a correspondingly larger proportion of the control period. Thus,

the corrective action of the motor rapid and effective when the speed differential is high, and yet, when the speed differential has been reduced to substantially the desired relationship, the adjusting motor operates at its low speed so as to reduce the possibilities of overcorrection.

As a. further aid in attaining rapid correction of unusally large variations in the diierentia-l speed of the two compared shafts, the relay 2361 may be constructed so as to possess slight slowto-'operate characteristics, for by this means the opening of the contacts may be so delayed that when the energizing periods for the relay are relatively short, as when such a high speed differential exists, the contacts will remain closed, and the entire period of adjusting operation of the motor 21E' will therefore be at high speed. In addition it will be observed that in the form shown in Fig. 6, the speed of corrective adjustment is not only varied in accordance with the magnitude of the speed variance which is to be corrected, but is also varied in accordance with the sense of the correction which is to be made.

In Fig. '7 of the drawings there is illustrated an embodiment of hydraulic actuator which may be associated with the two-way solenoid 30 i1- lustrated in Fig. 1A of the drawings, and this hydraulic actuator is adapted to be associated with mechanism such as that shown in Fig. l, in which instance a hydraulic motor 280 which forms a part of this hydraulic actuating mechanism would be substituted for motor 21 of Fig. l. The two-way solenoid 30 has two operating coils which act in opposite directions upon an armature 28|, and this armature is operatively connected to a balanced valve 282 which normally assumes a centered position within a valve casing 283. Hydraulic uid under pressure is supplied to the valve casing through an inlet 284 and it is adapted to be passed from the valve casing 283 selectively through outlet passages 285 and 286. The outlet passage 285 is connected to the hydraulic motor 280 so as to operate the motor in one direction, while the outlet passage 286 is connected to motor 280 to operate the same in the other direction. The two passages 285 and 286 have valves 281 and 288 respectively positioned therein so that the rate of flow to the motor 280 through these passages may be regulated. Thus by adjustment of the valves 281 and 288 the speed of operation of the motor 280 may be varied, and by such means the adjustment of the speed varying means, such as the controlled governing mechanism 26 of Fig. 1, may be attained at a faster rate when the speed of the engine is to be increased.

In Fig. 8 0f the drawings there is illustrated an embodiment of the invention whereby one of the engines of a two-motored airplane may serve I ,switch has brushes tended from the wire 4and as will anexas as a master engine and the speed of the other engine may be correlated with the master engine within relatively close limits. In 'this embodiment of the invention a master commutator switch MSB and a secondary commutator switch employed and these switches may be of an identical construction. The master switch M58 is arranged so that, the brush elements thereof are driven by a master shaft 20-5 while the brush elements of the secondary commutator switch S8 are driven by a secondary shaft 20-1, these shafts constituting driven elements of the master engine and the secondary respectively of theairplane. The secondary commutator 4i-5, 42-6 and 43-8 which correspond to the brushes included in the secondary commutator, as Si, of Fig. 1. Similarly arranged brushes are included in the master switch MS-B, but since this switch is to act as the-master, only one of these brushes is utilized and this brush is identified as 40-8 since it correspondsin function with the brush 40 of the embodiment of the invention shown in Fig. 1.

The commutator bars of the switches MSB and S6 are so arranged that diametrically opposite commutator` bars in each switch are electrically connected, and correspondingly located commutator bars of the two switches are electrically connected by wires indicated generally at. 315, there being connector plugs 316 and 311 interposed in the connecting wires 315 to facilitate installation of the apparatus.

The two commutator switches are 'associated j;

with a control unit CUB which is in many respects similar to the control unit CUIB shown in Fig. 3 of the drawings, and through this control unit, the operation of an adjusting motor 21-8 is con- -trolled so that a controlled governing mechanism such as the speed varying mechanism 28-5 may be operated in opposite directions. The speed governing mechanism may be arranged to adjust the fuel supply and hence govern the speed of a variable speed engine which drives the secondary shaft 20-1. In the present instance the motor. 21-8 is energized from a suitable source of current indicated at 318 and affording line wires 318 and 380, and these line wires are connected to the various elements of the apparatus through a control panel 38! which affords a manual control switch 382 through which the mechanism may be rendered operative or inoperative. The control panel 38| also includes signal lamps 383L and 38212l which are lighted selectivelyl as will hereinafter be the adjusting motor 21-8 has reached the limit of its travel in one direction or the other.

One side of the line wire 380 to the brush 40-8 of the master switch by means including a wire 384, this wire being extended through the plug socket 815. This same side of the circuit is extended by wires 385 and 335 to the common terminal of the field windings 381 and 883 oi the adjusting motor 21-8. The other side of the source 318 is ex- 318 through the switch 382 and a wire 389 to a terminal 330 of the control unit CUB, this connection being through a connector plug 33| to facilitate installation of the apparatus. Circuit is extended from the line wire 380 through the wire 385 and a wire 392 to another terminal 393 in the control unit CUB, be hereinafter explained in detail, the control circuits from the control unit CU5 to the eld windings of the motor 21-8 are arranged to include terminals 394 and 335 which .H5-8 andi minals 394 and 395 form partof the control unit CUB. Thus, wires i1-5 are extended from the terthrougn the connector plug 38| to the field windings 381 and 388 respectively. such wires being extended through a connectorl plug 398 at the motor 21-5. The wire IIB-4 is connected to the field winding 381 through a limit switch 391 which, when opened by operation of the motor to one limit of its' travel, is arranged to engage another contact which extends circuit through a wire 398 to the signal lamp 302B., and circuit from this lamp is continued to the line wire 380 by a Wire 333. A similar limit switch 400 is interposed 'between the wire ill-f8. and the field winding 388, and when this switch opens the circuit to the field winding. it is arranged to engage another contact which extends the circuit through a wire 40| to the signal lamp 383L. Thus when the motor reaches one limit of its travel, thiscondition is indicated by the lighting of the appropriate one of the two signal lamps, and the pilot may then readjust the manual control in the manner explained withl reference to Fig. 8 of my aforesaid parent application, thereby to enable the control apparatus to continue its automatic operation.

As hereinbefore pointed out, the switch S5 constitutes the secondary switch of the apparatus shown in Fig. 8,and wires 45, 46, and 41 are extended from the three brushes of this commutator switch in the same manner as in the embodiment of the invention shown in Fig. 1 of the drawings. These wires are extended through the connector plugs 311' and 39|, and in the control unit CUB, the wire is connected to a terminal 402, the

. wire 48 is connected to a terminal 408, and the wire 41 ls connected to a terminal 404.

The control unit CUB, being similar to the conmi una CUIB, has a master relay lsnH and two secondary relays iBiI-I and |82H, and these relays are connected and-related to each other in substantially the same manner as thethree relays of'Fig. 3. Thus, in general. it should be observed explained, to indicate that that circuits extended from the line wire 308 through the switch MSB and the switch S0 to the wires 45, 48 or 41, must be ext"ended through the relay to be operated and back to the line wire 382 through the manual switch 318. As to the master relay |60H, such a circuit is extended from the terminal 402 through a protective resistor 405 and a Wire 406 in series to one terminal of the coil of the master relay I60H, while means including a wire 2l4H connects the other side of the relay |60H through the relay contacts lliH and I8IH, in series, and thence lthrough a wire 401 to the terminal 380. The relay ISBH has means including a condenser iSiI-I connected across its terminals to impart predetermined slow-to-release characteristics thereto. The energizing circuit for the relay IBIH is extended from the terminal 403 by a wire 408 to a normally closed relay contact I15H of the relay 982K. from which a wire 202K extends circuit to one side ofthe relay coil. Similarly, the energizing circuit for the relay i62I-I includes a wire 403 from the terminal 404 to the normally closed relay contact |65H, from which a wire 20511 extends to one side of the relay i52H. Wires from the other two terminals of the relays ilH and I62H are connected to the relay contact 154K, while a wire'4lll extends from the contact |83H to the wire 401 to thus carry the circuit back to the terminal 390. Holding circuits for the relays ISIH and IH are provided by a wire 4H and branch leads 4I2 and M3 to normally open contacts of the respective relays IDIH and IG2H, so that these holding circuits extend through and are controlled -by the master relay contacts IB3H and I64H. These holding circuits are effective, s'o long as the relay contacts ID3H and I64H are closed, to hold the actuated one of the secondary relays in its actuated condition after the circuit through the Wire 4D or 41 has been broken.

In the embodiment of the invention shown in Fig. 8, a relatively long normal release time for the master relay ISDH is employed, such as two or three seconds, to thereby attain sensitivity of detection of undesired speed variation between the two shafts, and means are provided for reducing the normal release time of the master relay whenever one of the secondary relays is operated. This is accomplished by connecting electrical resistance across the terminals of the master relay coil. Thus, a. wire 2DIH, connected to the wire 406, has branch leads extended tothe stationary contacts of normally open relay contacts ISDH and I18H, and these contacts ISDH and I18H are connected through adjustable or variable resistances 2I8H and 2I1H, respectively, to a wire 4I4 which extends to the Wire 2I4H. Thus when the relay ISIH is energized, the contact I68H is closed and the resistance 2I8H is connected across the terminals of the master relay ISDH, while operation of the relay I62H similarly connects the resistance 2I1H across the master relay.

When the relay IBIH is thus energized, a contact I12I-I is closed, this contact being connected by a wire 4I5 to the terminal 394, and therefore circuit is extended from the contact I12H through the winding 381 of the adjusting motor 21-6 and to one side of the power source at 38D. The movable relay contact which thus engages the contact |12H is connected by a wire IDBI-I to the contact I8IH and thence through the wire 4D1 to the terminal 39D, thereby to complete circuit through the wire 389 and the switch 382 back to the other side of the line. The circuit for the other eld winding of the motor 21-6 is completed by closure of the relay contact I82I-I when the relay I62H is energized, the relay contact I82H being connected to the terminal 395 by a wire 4I6 and the movable contact which engages the contact I82H being connected to the wire 407.

Thus, the operation of the adjusting motor 21-6 is initiated in the appropriate direction by selective closure of the secondary relays ISIH or IEZI-I, and the operation of the motor is continued until release of the master relay ISDH breaks the holding circuit to the effective one of the secondary relays. Such periods of operation of the motor are so controlled, however, by the resistance 2I1H or 2I8H that objectionable over-correction is avoided despite the relatively protracted normal release period of the master relay ISDH. In the embodiment of the invention shown in Fig. 8, the provision for adjustability of the resistance 2I1I-I, as by an adjusting member 4I8, and for adjustment of the resistance 2I8H, as by an adjusting member 4I9, enables such control of the operation of the apparatus to be quickly and easily attained with respect to a particular installation. Thus the normal release period of the master relay ISDH may be established at an arbitrary and relatively large value in order that sensitivity of detection may be assured, and after installation of the apparatus, the apparatus may be adjusted by the adjustable devices 4I8 and 4I9 so as to attain the desired correlation Without over-correction or hunting. As an example, it may be found, upon initial operation oi a newly installed control apparatus, that the length of the operating period of the adjusting motor and the speed at which the motor operates the governing mechanism will cause over-correction where the detected speed differential is slight, and when such operation is noted, corrective adjustment may be made upon the resistances 2 I 1H and 2I8H so as to decrease the amount 'of resistance which is thrown across the terminals of the master relay. Such reduction in the effectiveness of these rsistances enables more rapid dissipation of the charge in the condenser ISIH and this results in reducing or shortening the normal release time, and hence the apparatus may be readily set so as to attain the desired correlation without over-correction. It will be observed, of course, that the amount of resistance thus thrown across the terminals of the relay should be kept as large as is consistent with elimination of over-correction, for by so doing the time required to correct large speed dinerences will be minimized.

In Fig. 9 of the drawings there is illustrated another embodiment of the invention whereby correlation of the4 two engines of a two motored airplane may be attained in such a manner that one of the engines serves as a master with which the speed of the other or secondary` engine is correlated. This embodiment of the invention is adapted particularly for use where the speed correlation and adjustment is attained through the use of variable pitch propellers, although in most of its aspects, this embodiment of the invention might be used with equal effectiveness for adjusting the fuel supply of the engines so as to control and correlate the engine speeds. Thus, the master engine has a. master shaft 2D-8 the speed of which may be adjusted by a propeller pitch varying means 42D associated with the propeller of the master engine and driven by a reversible motor 26-8 of the construction shown in Fig. 8. Similarly, the secondary engine has a secondary shaft 2D-9 which may be controlled and adjusted as to speed by a propeller pitch varying means 42| associated with the propeller of the secondary engine and driven by a motor 26-9 of the construction shown in Fig. 8.

The master shaft 2D-8 and the secondary shaft 2D--9 have commutator switches MST and S1 respectively :associated therewith, such switches both being of the same construction as the switch are driven by their respective shafts 2D-8 and 2D-9. In the secondary switch S1 the three brushes have been identied as III-1, 42--1 and 43-1 so as to conform with the identiflcation used in Fig. 8; and similarly the one brush of the master commutator switch MS1 which is utilized is identied as 40-1. The other two brushes of the master switch MS1 are left in position. The same condition of course applies to the embodiment of Fig. 8.

The commutator bars of the two switches MS1 and S1 are connected by means including wires 315K and connector plugs 316K and 311K in the general manner disclosed in Fig. 8, it being noted, however, that the connections within the switches MS1 and S1 include slip ring arrangements as shown in Figs. 10 to 12 of my aforesaid parent application. Similarly, the three brushes of the secondary switch S1 are connected through the plug 311K and wires 45, 46 and 41 to a control unit CUSK of the construction shown in Fig. 8.

27 This control unit has corresponding terminals, and the wires 45, 48 and 41 are connected through the plug SSIK to the terminals 402K, 408K and 404K, respectively.

In the embodiment shown in Fig. 9 the circuit is energized from a power source such as a battery 818K which has one side thereof connected by wire 425 to the terminal 393K of the control unit CUBK. The other side of the battery 818K is associated with the mechanism through a switch panel 428 which includes a two-way switch 421 Iand a three-way switch 428. Thus the other side of the battery 318K has a, wire 428 extended therefrom with branch leads to the common terminals of the two switches 421 and 428. 'Ihe switch 421 has one stationary contact 480 connected by a wire 45| to the field winding 881K of the motor 255, while the other contact 482 of the switch 421 is connected by a wire 453 to the eld winding 888K of the motor 25-8. A wire 484 is extended from the wire 425 and in series through wires 435 and 438 to the common terminal of the two eld windings of the motor 25-8, and hence by manual closure of the switch 421 selectively to the contact 430 or the contact 432. the motor 25-8 may be operated in either direction selectively to produce the desired adjustment of the propeller oi the master engine. This will, of course, vary the speed of the master engine and its shaft 2li-8. The motor 28-8 has limit switches through which the wires 43| and 483 are connected in the same general `manner as in the embodiment shown in Fig. 8, and when either of these limit switches is opened, 4c/warning circuit is extended through a wire 438 to a signal lamp 439 which is connected at its other side to the wire 434.

Generally similar manually controlled connections are provided for themotor 2li-9, there being a contact 440 in the switch 428 which is connected by a wire 44| to one side of one of the iield windings of the motor 25-9 through its associated limit switch. The switch 428 also has a contact 442 which is connected by a, wire 443 to one end of the other field winding of the vmotor 25-9 through the related limit switch, and the common terminal of the motor 25-9 is connected by a wire 444 to the wire 434. When either one of the limit switches of the motor 26-9 is opened, a

circuit is closed through means including a wire 445 through a signal lamp 445 and back to the wire 434. Thus by closure of the switch 428 to one of the contacts 44| or 442,*the -adjusting motor 25-8 may be operated in either direction to adjust the pitch of the propeller of the secondary engine, thereby to cause the speed of the secondary engine to be varied.

When the control apparatus of the present invention is to be rendered operative, the switch 425 is closed to a contact 455 which is connected through a Wire 45| to the terminal 885K of the control unit CUSK. When this is done the relays oi' the control unit are rendered operative, and circuit may be extended thereby to the terminal 394K or 395K selectively. When circuit is thus extended to one of these two control terminals, this embodiment of the invention is arranged to control circuit to the windings of the motor 25-9 selectively, and in accomplishing this result, a two-way or balanced relay 452 is utilized. This relay 452 has an actuating coil 458 which is operable to move the contact 454 of the relay into engagement with the contact 455 which is provided in the wire 443, and a similar coil 455 is provided in the relay 452 which is operable to draw the contact 454 into engagement with a 28. v contact 451 which is connected to the wire 44|. The contact 454 of the relay 452 is connected by a wire 458 to the wire 428 so that when the contact 454 is engaged with one or the other of the contacts 455 and 451, circuit is completed to one or the otherof the eld windings of the motor 25-9.

vThe relay coils 453 and 455 are controlled by the control unit CUSK, the terminal 394K of the control unit being connected by a wire 450 to one terminal of the relay coil 453, while the terminal 395K is connected -by a wire 45| to one terminal of the relay coil 456. The other terminals of these two relay coils are connected by meansI including a wire 452 to the wire 425. Hence when circuit is extended to the terminal394K, the relay coil 455 is energized so as to cause circuit through the contact 455 to one of the field windings of the motor 25-8, while completion of a circuit to the terminal 395K energizes the rlay coil 456 and causes circuit to be completed through the contact 451 to the other field winding of the motor 25-9. Condensers 465 and 455 are connected across the terminals of the relay coils 453 and 456 to thereby impart slow-to-release characteristics thereto and'obtain the resulting advantages described in connection with the relay |30 of Fig. 2. Thus the control mechanism of the Fig. 9 operates to adjust the speed of the secondary shaft 20-9 to conform the speed of the master shaft 2li- 8. The speed of the master shaft 20-8 may of course be varied from time to time by manipulation of the manual control switch 426, and in such an event the control apparatus operates to adjust the speed of the secondary shaft 20-9 to conform with the newly established speed of the master shaft.

It will be observed that in the embodiment of the invention shown in Figs. 1 to 4 of the drawings, the values of the resistances which control the reduction of the release time of the master relay have been shown as having fixed values, and in high production manufacture of the control apparatus for use with equipment of a particular design, suchiixed values for such resistors serve to attain the desired functioning of the control apparatus so as to cause proper speed correlation. However, where varying conditions of use or possible variations in the operating characteristics of the equipment are possible or expected, these controlling resistances may be made variable or adjustable as taught in connection with the embodiments of the invention disclosed in Figs. 8 and 9. Such variable or adjustable characteristics may, of course, be utilized even though the resistances are to be of different values in respect to opposite directions of operation of the speed adjusting means. Thus in any event, whether these control resistances are of fixed value or are adjustable in character, their controlling action in governing the characteristics of the control impulses to the speed governing means enables the control apparatus to be used with any particular speed adjusting means without change or modification of the speed adjusting means.

In view of the foregoing description it will be apparent that the present invention enables control apparatus for correlating or controlling the speed of one or more shafts or the like to be readily adapted to the equipment with which it is to be used, and hence, without redesign or modification of such equipment, the control apparatus of this invention will function to attain the desired speed correlation or control. Moreover, it will be apparent that with the control apparatus of the present invention, the desired accuracy of speed correlation or control may be attained under the varying circumstances which involve variations in the nature or type of the associated equipment or where varying conditions are encountered in use. Furthermore, the ability oi' the present control apparatus to variably control and variably adjust the speed of one or more engines or the like is of particular utility in aviation uses, for through the functioning of the present apparatus the operation and control of an airplane is materially simplified whether the airplane be of the single motor type or the multimotor type. Thus, in a single motored airplane, the maintenance of the engine speed at a predetermined standard established independently of the load avoids the necessity for manual control and readjustment of engine speed during rapid changes of flight attitude which would otherwise tend to violently race the engine of the airplane. In airplanes having two or more engines the control apparatus has this same beneficial effect where an electric motor or the like is used as the speed standard; and in such airplanes,A whether the speed standard is set by an independent electric motor or by one of the engines, the control apparatus serves to afford a single manual control for the plurality of engines, thereby to simplify the `operation of the airplane. The maintenance of synchronism of the several engines of the airplane also has other beneficial results, for it reduces deviation from the desired course which might result from unbalanced application of driving power, and is helpful under conditions where formation of ice on one or more propellers would otherwise reduce engine speed or cause lack of synchronism of 'the engines.

It will also be evident that the control apparatus of the present invention is of such a character that many diicult and widly varying problems of synchronization or speed control may be handled thereby, for the present control apparatus not only is readily adaptable to the varying types of speed adjusting means which may be encountered but is also of such a character that it compensates for differences in the response of the controlled apparatus due to load or the like. Moreover, the speed adjustments attained with the present apparatus are directly.

related to the magnitude of the speed differential which is to be corrected, and this is accomplished despite the fact that the detecting means of the control apparatus is sensitive to extremely small speed variations.

Thus, while I have illustrated and described the preferred embodiments of my invention, it is to ibe understood that these are capable of variation and modication and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a control apparatus for correlating the rotative speeds of relatively rotatable elements such as independently driven shafts, a master shaft andvariable speed driving means therefor, an independently rotatable secondary shaft, a variable speed engine for driving said secondary shaft, means operable in two directions for varying the speed of said engine to selectively increase or decrease the speed thereof, means operatively associated with said shafts and operable to detect undesired variation in the speed relationship of said shafts and to determine the sense of such variation, and means controlled by said detecting means in response to any selected magnitude of speed variance that is detected to actuate said speed varying means inl one amount and in a corrective direction when the detected speed of said secondary shaft is greater than the desired speed and in a greater amount and in the opposite corrective direction when the detected speed of said secondary shaft is less than the desired speed.

2. In a control apparatus for correlating the rotative speeds of relatively rotatable elements such as independently driven shafts, a master shaft and variable speed driving means therefor,

an independently rotatable secondary shaft, a

variable speed engine for driving said secondary shaft, means operable in two directions for varying the speed of said engine to selectively increase or decrease the speed thereof, means operatively associated with said shafts and operable to detect undesired variation in the speed relationship of said shafts and to determine the sense of such variation, and means controlled by said detecting means in response to any particular magnitude of speed variance that is detected to actuate said speed varying means for an operating period of one length and in a corrective direction when the detected speed of said secondary shaft is greater than the desired speed and in the opposite corrective direction and for an operating period of greater length when the detected speed of said secondary shaft is less than the desired speed.

3. In a control apparatus for correlating the rotative speeds of relatively rotatable elements such as independently driven shafts, a master shaft and variable speed driving means therefor, an independently rotatable secondary shaft, a variable speed engine for driving said secondary shaft, means operable in two directions for varying the speed of said engine to selectively increase or decrease the speed thereof, means operatively associated with said shafts and operative to detect undesired variation in the speed relationship of said shafts and to determine the sense of such variation, and means controlled by said detecting means in response to any particular magnitude of speed variance that is detected to actuate said speed varying means selectively in opposite directions and at one speed when the detected speed of said secondary shaft is greater than the desired speed and at a greater speed when the detected speed of said secondary shaft is less than the desired speed. A

4. In a control apparatus for correlating the rotative speeds of relatively rotatable elements such as independently driven shafts, a master shaft and variable speed driving means therefor, an independently rotatable secondary shaft, a variable speed engine for driving said secondary shaft, means operable in two directions for varying the speed of said engine to selectively increase or decrease the speed thereof, means operatively associated with said shafts and operable to de,- tect the presence and the sense and magnitude of undesired variation in the speed relationship of said shafts, and means controlled by said detecting means in response to any particular magnitude of speed variance that is detected to actuate said speed varying means through corrective adjustments in different amounts such that a corrective ajustment to increase the speed of said secondary shaft is of greater magnitude than a corrective adjustment to decrease the speed of said secondary shaft.

ROSSER L. WILSON. 

